1. Field of the Invention
The present invention generally relates to an improved rotor of a rotary electric machine such as a vehicle alternator to be driven by an internal combustion engine of a vehicle, for example.
2. Description of the Related Art
The Lundell type rotor core of a rotor in an ordinary available vehicle alternator has a boss portion, disk portions (or pole cores), and a pair of pole cores. Through the boss portion a field magnetic flux flows in the axis direction of the rotor in the inside area of a field coil and in the radial direction of the field coil. The disk portions, that are formed extended from both the outer end of the boss portion in the axis direction toward the outer end of the boss portion in the radial direction, provides the field magnetic flux in the radial direction of the rotor. Each of a pair of the pole cores has plural claw poles extending axially from outer periphery of the disk portion in the radial direction of the rotor so that the plural claw poles accommodate the field coil wound on the outer peripheral surface of the boss portion. The field magnetic flux is transferred between the plural claw poles and the stator core.
Each claw pole in one pole core and the corresponding claw pole of the other pole core are placed alternately in the circumferential direction of both the pole cores. Such an ordinary Lundell type rotor core is manufactured by facing a pair of the pole cores to each other and then assembling them in the axis direction of the rotor. Each of the pole cores is made of soft magnetic core of an ingot shape.
Such an ordinary Lundell type rotor core involves a drawback to generate large wind noise and to cause windage loss while the rotor core rotates at a high speed rotation because the claw poles of the pole core are exposed in the radial direction of the field coil in the outer space of the field coil wound on the boss portion of the rotor.
In order to avoid such a drawback described above, prior documents, the Japanese patent laid open publications No. 2002-247817 and No. 2005-27415 have disclosed a mechanism to form a magnetic-pole cylindrical portion that covers the outside of the field coil in the radial direction (hereinafter, the rotor core having such a mechanism will be referred to as “a Lundell type rotor core having a magnetic-pole cylindrical portion”, and the cylindrical portion has a hollow cylindrical shape.)
Because each of the plural claw poles in such a Lundell type rotor core is not exposed in the outer space in the radial direction of the field coil, it is possible to reduce wind noise generated at each claw pole. In more detail, the Lundell type rotor core with the magnetic-pole cylindrical portion has the boss portion, a pair of the disc portions, and the magnetic-pole cylindrical portion. Through the boss portion a field magnetic flux flows in the axis direction of the rotor in the inside area of the field coil and in the radial direction of the field coil. A pair of the disk portions, that is formed extended from both outer ends of the boss portion in the axis direction thereof toward the outer end of the boss portion in the radial direction thereof, provides the field magnetic flux in the radial direction of the rotor. The magnetic-pole cylindrical portion is placed or mated between a pair of the disk portions in the outside area in the radial direction of the field coil, and through the magnetic-pole cylindrical portion, the field magnetic flux flows in the axis direction. The field magnetic flux is transferred between the stator core and the magnetic-pole cylindrical portion.
The prior document, the Japanese patent laid open publication No. JP 2002-247817, has proposed to form all of the boss portion, the disk portions, and the magnetic-pole cylindrical portion in the Lundell type rotor core by magnetic steel sheets that are laminated in axis direction. The prior document, the Japanese patent laid open publication No. JP 2005-27415, has proposed to form all of the boss portion, the disk portions, and the magnetic-pole cylindrical portion of the Lundell type rotor core by a soft magnetic core of an ingot shape.
In more detailed explanation, the prior document, the Japanese patent laid open publication No. JP 2005-27415, has adopted the mechanism in which the magnetic-pole cylindrical portion made of such a soft magnetic core of an ingot shape is supported in the axis direction by a first pole core and a second pole core (hereinafter, each pole core will be referred to as “side core”). The first side core has a half boss portion and a disk portion made of soft magnetic core of an ingot shape. Like the first side core, the second side core has a half boss portion and a disk portion made of soft magnetic core of an ingot shape.
However, the magnetic-pole cylindrical portion in the Lundell type rotor core disclosed in the prior document, the Japanese patent laid open publication No. 2002-247817, involves a drawback that increases a space in an electromagnetic circuit in an electric rotary machine, and further increases an reluctance (or a magnetic resistance) and amount of a field current because a penetrate direction of magnetic flux is approximately equal to the direction of the laminated magnetic steel sheets. Further, this prior technique involves a drawback to decrease a stiffness of the rotor core. In more detailed explanation, although the torque of the rotary axis of the rotor is transmitted to the magnetic-pole cylindrical portion through the boss portion and the disk portions, each magnetic steel sheet forming the boss portion and the disk portions made of the magnetic steel sheets in axis direction is shifted towards the circumference direction when the torque is transmitted. Thus, this prior technique has essentially a small torsional stiffness
Further, the conventional technique, the Japanese patent laid open publication No. 2005-27415, has a manufacturing limitation of a small allowable-dimension tolerance of each of both the side cores and the magnetic-pole cylindrical portion and a difficulty to satisfy a necessary manufacturing accuracy because its Lundell type rotor core is made of soft magnetic core of an ingot shape. This drawback increases the manufacturing cost of the Lundell type rotor core.
Still further, more specifically, the end surfaces of both the half boss portions are faced to each other in the axis direction of the rotor core, and the magnetic-pole cylindrical portion are accommodated in the space between the half boss portions of the side cores. A small gap is formed between the half boss portions of the side cores or between the magnetic-pole cylindrical portion and the disk portions unless the necessary dimension tolerance in the axis direction is satisfied. Such a presence of the gap decreases the stiffness of the rotor core and also increases the necessary amount of a field current because of increasing the reluctance (or the magnetic resistance). It is therefore important matter to eliminate the gap formed between the half boss portions of the side cores faced to each other.